1. Field of the Invention
This invention relates to magnetic markers for electronic surveillance of recorded media; and more particularly to the identification of pre-recorded or recordable disks, such as compact disks, digital video disks, laser disks and the like, as well as cartridges or cassettes and the like, by magnetic markers of electronic article surveillance systems, based on magnetic harmonic generation and detection.
2. Description of the Prior Art
Inventory control is a major consideration in wholesale and retail sales. Inventory control includes anti-theft and anti-pilferage considerations so to minimize lost profits. Various devices and various techniques are known to limit theft and recently amongst the most successful are the use of electronic article surveillance systems (xe2x80x9cEASxe2x80x9d), which include a marker affixed to an item, and a sensor means that can detect the marker. Typically, such sensor means are devices which are strategically placed in suitable locations, often described as xe2x80x9cinterrogation zonesxe2x80x9d i.e., points of entry or exit where wholesale and retails sales may take place, or locations through which the transport of vendible articles may occur.
Currently there are two EAS systems in wide use that employ techniques based on magnetics. A first technique involves detecting higher harmonic signals generated by a magnetic marker excited at a given fundamental frequency. In this case higher harmonics are integral multiple of the fundamental frequency. There are, therefore, a number of different methods of operations that are conceivable depending on the needs and objectives for the envisaged types of surveillance. Advances in this class of technology have been made, including the development of markers whose performance is not affected when they are flexed or bent. Such are known, for example in U.S. Pat. No. 4,553,136. A second technique is based on the magneto-mechanical properties of magnetostrictive strips that are used as markers. Examples of this second technique are disclosed, for example, in U.S. Pat. No. 4,510,489 and 4,510,490.
The present invention relates to the former class of EAS systems, viz., those based on magnetic harmonics. In such systems, a magnetic marker comprising of one or more magnetically xe2x80x9csoftxe2x80x9d strips is excited in an interrogation zone by an external oscillating magnetic field at a fundamental frequency. Because of the non-linear magnetization behavior of the soft magnetic strip or strips in the marker, the magnetic response may be measured as an electrical signal that is detectable by the sensor means in the interrogation zone. The electrical signal detected by the sensor means in the interrogation zone contains both higher harmonic signals as well as a signal at the aforesaid fundamental frequency. According to this technique, by selecting a specific harmonic signal to track, the sensor means in the interrogation zone may identify the magnetic state of the magnetic marker, (i.e., xe2x80x98activatedxe2x80x99, or xe2x80x98deactivatedxe2x80x99). When such a magnetic marker is xe2x80x98activatedxe2x80x99, the sensor means may sense such a condition and may in turn trigger an alarm when an unauthorized vendible article is placed in the interrogation zone. Such a magnetic marker is normally in an activated state and can be used repeatedly. When it is desired to permit a vendible article bearing a marker safe passage through the interrogation zone, the marker must be deactivated. Typically, when deactivation is needed, a magnetically semi-hard magnet or magnets are attached to, or placed in close proximity with the soft magnetic strip or strips. Deactivation is accomplished by simply magnetizing the semi-hard magnet or magnets, which magnetically saturate the soft magnetic strip or strips, resulting in essentially no higher harmonics in the detection signal. The presence or absence of higher harmonics in the detection signal, detectable by the sensor means, determines the nature of the article in the interrogation zone, thereby establishing a condition which can be used to determine if an alarm or other indicator should be activated or deactivated. Such a marker may be used many times as it is readily re-activated by demagnetization of the semi-hard magnetic piece or pieces which, in turn, will desaturate the magnetically soft strip or strips of the marker.
Markers which include only one or more magnetically soft strips without semi-hard magnets, as well as those which include semi-hard magnets in contact with, or in near physical proximity to one or more magnetically soft strips are known to the art.
Such EAS markers described above have been used for surveillance of many types of vendible articles. Typically they are conveniently provided as small tags, strips or casings which include the requisite one or more magnetically soft strips and optionally but very frequently also include one or more semi-hard magnets in contact with, or in near physical proximity to one or more magnetically soft strips. Such markers are very conveniently adhered to a vendible article or its packaging or can also be hidden within the interior of the same. Such markers are very cost effective and have found widespread use in inventory control of many classes of vendible goods.
However, the use of such markers has met with only limited success when used with pre-recorded or recordable media. By way of non-limiting example these include; disk media such as compact disks (xe2x80x9cCDxe2x80x9d, xe2x80x9cCD-Rxe2x80x9d, xe2x80x9cCD-RWxe2x80x9d), digital video disks (xe2x80x9cDVDxe2x80x9d), larger formatted laser disks (xe2x80x9cLDxe2x80x9d) and the like, as well as cassette media which includes videocassettes (such as xe2x80x9cVHSxe2x80x9d full-size and micro cassettes) and recordable or prerecorded audio cassettes as well as DAT cassettes, and the like. Generally markers are placed on the packages containing these media, which however can be easily circumvented. For greatest effect in inventory control, markers are ideally attached directly to the recordable/recorded media. U.S. Pat. No. 5,699,047 discloses certain such markers, and recites that these markers can be used for disks which have one, or two optically recorded surfaces. Unfortunately, the magnetic strips placed on a disk with two optically recorded surfaces according to the teachings of U.S. Pat. No. 5,699,047, however, are not properly configured so that effective surveillance is difficult to achieve.
In certain embodiments described in U.S. Pat. No. 5,699,047, the marker strips are essentially magnetically closed, due to magnetic proximity of the two strips. Therefore, in such a configuration the marker strips do not emanate a sufficiently strong magnetic field outside the disk area in response to a sensor means in a typical interrogation zone. Detection of the presence of a marker at some distance from the sensor means becomes increasingly difficult as the distance increases. In a typical surveillance system, this distance between the marker and the detecting coil typically used in the sensor means is of the order of 1 to 2 meters. Where the excited magnetic field from the marker is insufficiently strong, as may be the case with the embodiments described in U.S. Pat. No. 5,699,047, the marker may pass through the interrogation zone undetected.
Accordingly there is a real and continuing need in the art for improved markers for electronic article surveillance systems which may be directly attached to recordable or recorded media. Especially needed are improved markers for electronic surveillance of optically recorded or recordable media such as compact disks, digital video disks, larger formatted laser disks, and the like.
There is also a real and continuing need in the art for improved inventory control techniques which employ electronic article surveillance systems, and improved markers which may be directly attached to recordable or recorded media.
There is also a real need in the art for improved media, either pre-recorded media, or recordable media, that comprises an improved marker capable of being sensed by electronic article surveillance systems.
There is a further need in the art for improved media, either pre-recorded media, or recordable media, which includes an improved marker integrated into the construction of the aforesaid media, the improved marker being capable of being sensed by electronic article surveillance systems.
There is also a need in the art for an improved method for manufacture of either pre-recorded media or recordable media, which method includes the step of associating directly with the such media an improved marker capable of being sensed by an electronic article surveillance system.
There is also a real need in the art for improved methods for manufacture of either pre-recorded media or recordable media, which method includes the step of integrating an improved marker capable of being sensed by electronic article surveillance systems directly with the aforesaid media during or subsequent to the manufacture of the aforesaid media.
These and other objects of the invention are fully met by one or more features of the invention described herein.
The present invention provides an improved marker having high detection sensitivity and especially suited for use with harmonic responsive electronic article surveillance systems. The improved marker has an elongated configuration. It makes use of the higher harmonic response of xe2x80x98softxe2x80x99 magnetic materials, especially ferromagnetic amorphous metal strip or strips, that is generated when the strip is placed in the unrecorded area of recorded media, as well as in corresponding areas of recordable media which are capable of being recorded at a future time. As used herein, the term xe2x80x9crecorded mediaxe2x80x9d includes compact disks, laser disks, digital videodisks and the like, as well as cartridges or cassettes and the like. The term xe2x80x9celongatedxe2x80x9d, as used herein, means that the marker has an aspect ratio of at least 20, preferably ranging from about 50 to 900, and most preferably from about 100 to 650. Elongated markers having these aspect ratios have a length typically ranging from about 30 mm to 180 mm, and preferably from about 50 mm to 170 mm, and more preferably from about 70 mm to 160 mm. Markers having aspect ratios of about 100 to 650 and lengths of about 70 mm to 160 mm generate strong signal voltages in the presence of an applied magnetic field, and are readily detected in a highly reliably manner. For these reasons, such markers are especially preferred.
In accordance with the present invention, a synergy produced by combining certain xe2x80x98softxe2x80x99 magnetic materials and the marker""s configuration maximizes detection sensitivity. Examples of particularly useful soft magnetic materials suited for the present invention include commercially available amorphous metals such as METGLAS(copyright) 2714A, METGLAS(copyright) 2705M, METGLAS(copyright) 2827A and the like. These soft magnetic materials are commercially provided in long strips or ribbons; but are readily cut into appropriately configured shapes especially suited for use with the present invention in the manner described hereinafter. Ferromagnetic amorphous metals of the class described herein exhibit high magnetic permeabilities and low coercivities. Markers of the present invention having these alloy attributes produce large harmonic signal responses which may be readily detected by sensor means of electronic article surveillance systems. It will be understood by those skilled in the art that although these amorphous metals, or xe2x80x9cglassy alloysxe2x80x9d as they are often interchangeably referred to, are preferably utilized in the improved markers of the invention, other magnetizable materials that provide suitably high magnetic permeabilities and suitably low coercivities may also be used. Such materials are considered to be within the scope of the present invention, as defined by the subjoined claims. Amorphous metal strips exhibit excellent magnetic softness and ductility, and are readily shaped or cut. For these reasons, ferromagnetic amorphous metals are preferred.
In one aspect of the invention, there is provided an improved inventory control method wherein the improved markers, appointed for detection by an electronic article surveillance system, are attached to recordable or recorded media. In this method, the improved markers are directly associated with the prerecorded or recordable media. The markers are interrogated by an interrogation field of a preselected frequency in an interrogation zone in order to determine the status of the said marker. In the interrogation zone the marker is subjected to an oscillating magnetic field having a preselected frequency, also referred to as the interrogation field, and the magnetic response of the marker is detected by a sensor means. The sensor means typically includes a detecting coil in the interrogation zone. However, it may comprise any other device so long as the sensor means is capable of detecting signals containing higher harmonics of the aforesaid given frequency of the interrogating field. The improved inventory control method comprises of the steps of (a) subjecting an improved marker directly attached to recordable or recorded media to an interrogation field; (b) comparing detected signal or signals of the marker as it is subjected to the interrogating field; and (c) comparing the detected signal or signals to a predetermined signal characteristic, such as determining whether the detected signal or signals contain higher harmonics of a given frequency. A further optional step comprises providing information related to the surveillance status of the improved marker directly attached to recordable or recorded media which may be used to signal a further device, such as an alarm, a counter, and the like.
In still further aspect of the invention there are provided improved methods for the manufacture of recordable or recorded media. Such methods include directly affixing an improved marker to the surface of such recordable or recorded media, or embedding it therewithin. The steps of these improved methods may be carried out during or subsequent to the manufacture of the recordable or recorded media. Each of the affixing and embedding steps, as well as their beneficial effects are applicable to either recordable or recorded media.